The widow of suspect Tamerlan Tsarnaev is "doing everything she can to assist with the investigation," of the Boston Marathon bombing, attorney Amato DeLuca said in a statement Tuesday.

Katherine Russell last saw her husband Thursday, just hours before he died in a gun battle with police, according to a source close to the family. She was handing off her 2-year-old daughter to stay with him while she went to work, the source said.

The FBI wants to interview Russell about her husband, but for now, agents only have been able to talk to her lawyer.

"She knew nothing about it at any time," DeLuca told CNN's Chris Lawrence, referring to the bomb plot.

Russell, 24, learned through news reports that the father of her daughter was suspected in the attack, DeLuca said. "That's my understanding."

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"The reports of involvement by her husband and brother-in-law came as an absolute shock to them all," DeLuca's Tuesday statement said. "As a mother, a sister, a daughter, a wife, Katie deeply mourns the pain and loss to innocent victims -- students, law enforcement, families and our community. In the aftermath of this tragedy, she, her daughter and her family are trying to come to terms with these events."

"The whole family is a mess, to put it bluntly," he said Monday. "They're very distraught. They're upset. Their lives have been unalterably changed. They're upset because of what happened, the people that were injured, that were killed. It's an awful, terrible thing."

Tsarnaev's domestic violence arrest

Tsarnaev and Russell met when she was a student at Suffolk University in Boston, although it is unclear when they began dating. The couple married on June 21, 2010, according to marriage records at the Cambridge City Hall.

Eleven months earlier, Tsarnaev was arrested, accused of domestic assault and battery against his girlfriend at his home in Cambridge, police records said.

The police report was redacted to hide the girlfriend's name, and a police spokesman would not confirm it was Russell.

The woman, who was "crying hysterically," called 911 to report that she was "beat up by her boyfriend" on the afternoon of July 28, 2009, Cambridge Police Officer Angela Pereira wrote in the arrest report.

Tsarnaev told Pereira and another officer that his girlfriend "was yelling at him because of another girl."

"I asked the suspect if he had hit the victim, and he stated 'Yes, I slapped her,' " Pereira wrote.

The girlfriend told police Tsarnaev hit the left side of her face. "No visible marks were seen," Pereira said.

NPR's Laura Sullivan reported Friday on an interview with unnamed women she described as Russell's close friends and college roommates.

"They described Tamerlan as very controlling and very manipulative of their friend," Sullivan said. "They say he was combative and angry. He would often call (Russell) names and insult her. He would call her a slut and a prostitute, and they remember fights that they would get into where he would fly into rages and sometimes throw furniture or throw things."

Russell dropped out of school after she became pregnant in her senior year, the women told Sullivan. "They say that she really pulled away from her friends, that she cut off contact with them, and she also cut off contact with her family members which her friends had been in contact with," she reported.

Russell was born and raised in suburban Providence, Rhode Island, a Christian who converted to Islam after marrying Tsarnaev. She's an observant Muslim and wears a headscarf, her lawyer said.

Katie -- that's what family and friends call her -- is staying now with her parents in North Kingstown, Rhode Island, but before last week she was living in Cambridge and working as a home health aide, he said. "She worked many, many hours."

Her husband took care of their daughter each day while she was at work, her lawyer said.

"She would go off in the morning, she would work 'til late at night," he said. "She called to see how her daughter was and that kind of stuff, like any person would."

The Russell family hired DeLuca on Saturday, after federal agents contacted them asking to interview her, he said. For now, he is the one speaking to the FBI.

"She understands the need for doing it," he said. "This is the way the government looks at it, and she understands this. It's a threat to national security, and she gets that. And she's a really good person, very sympathetic to that. Katie's just trying to bring up her daughter."

In the statement released Tuesday, DeLuca said Russell is very close to her family.

"She is fortunate to have the support of her loving family now, as they, too, struggle to come to terms with these events and the deep sorrow we all feel following the events of last week," he said. "The injuries and loss of life -- to people who came to celebrate a race and a holiday -- has caused profound distress and sorrow to Katie and her family."

The family released its own statement Friday, after learning Tsarnaev had died.

"Our daughter has lost her husband today, the father of her child," the family said. "We cannot begin to comprehend how this horrible tragedy occurred. In the aftermath of the Patriots' Day horror, we know that we never really knew Tamerlan Tsarnaev. Our hearts are sickened by the knowledge of the horror he has inflicted. Please respect our family's privacy in this difficult time."